You should honor whoever the dogs decide is alpha. I know its hard since you were expecting Sadie to be alpha, but its looking like Cincy has a much more dominate personality. If this is the case, I'd start feeding, petting, etc Cincy first.

Some dogs have very vocal play. Lolly growls constantly while playing.

It sounds like you guys are doing the right thing by letting them work it out, but if you're worried its not play, try treating Cincy as alpha for awhile. Maybe then she will stop the struggle since she'll have the position she wants.